1. Field of the Invention
The present invention is related to devices for controlling fluid flow through a passage, and more particularly the devices for automatically shutting off fluid flow therethrough.
2. Description of the Prior Art
It is well known that natural gas is a clean and relatively inexpensive fuel source. As such, gas distribution systems have been widely installed throughout the United States and the world. To supply end users, such as commercial and residential consumers, pipelines are typically branched off of a main gas line to provide service to the individual end users. These pipelines are connected to a gas meter and therefrom branched to individual gas appliances and the like.
Because of the high flammability of natural gas, unrestricted escape of gas at the user end caused by the rupture or the severing of a pipeline can create a very hazardous and dangerous situation. Should a large quantity of gas be allowed to escape and fill a confined space, exposure to a spark or ignition source may explosively ignite the gas causing destruction to property and life. Therefore, it is desirable to include safety devices in the gas distribution system that automatically stop or restrict the flow of natural gas should the pipeline burst, a pipe fitting become dislodged, or an event occur causing an excess flow of gas.
Many shut-off devices have been developed over the years, and by way of example, one shut-off device of this type is disclosed in U.S. Pat. No. 4,257,452 to the assignee of the present invention. The shut off device of this type may be telescopically received in a pipeline and includes a poppet valve having a head biased upstream from a valve seat. Flow through the valve is arranged so that it impinges on the head to move the head toward the valve seat and close off fluid flow through the poppet valve when an excess flow condition occurs. Although this arrangement provides effective fluid flow control, the head has a tendency to oscillate under certain flow conditions. Therefore a damping arrangement was included in effort to prevent undue oscillation of the head during operation. Furthermore, when installed in the pipeline, this shut-off device could be misaligned which caused otherwise normal fluid flow across the device to be disturbed leading to possible improper operation of the shut-off device. Although the prior art shut-off valve by such assignee has enjoyed much success in the marketplace, it has been found desirable to provide a shut-off device that has a less complicated construction facilitating ease of assembly, which in turn reduces manufacturing costs, while still maintaining effective excess fluid flow control and shut-off characteristics.
Hence, those skilled in the art have recognized the need for a shut-off device for disposition in fluid distribution pipelines. It is desirable that such device incorporate a minimum number of components to facilitate ease of assembly which, in turn, lowers manufacturing costs. In addition, such a device should be constructed for convenient field installation in new or existing fluid distribution pipelines. The present invention meets these needs and others.